1. Field of the Invention
This invention relates to cameras which have made full use of the feature that the photographic lens has an axially movable lens such as a zoom lens and, more particularly, to optical systems which, though getting the camera imparted with a plurality of functions, enable the size of the camera to be minimized.
2. Description of the Related Art
Recently, technology is rapidly developing. Accordingly, cameras have many functions in an increasing variety of forms, and their use is being widely spread.
These may be classified by the type of finder used therein. According to this classification, the cameras are divided into two groups, one of which has the TTL (Through-The-Lens) type finder, so-called single-lens reflex cameras, and the other of which has the external type finder, so-called lens-shutter cameras. Another classification is based on the recording medium, giving cameras using a silver-halide film and video cameras using a CCD, or the like, photoelectric transducer means so that pictures have to be reproduced electrically.
In the former classification, the camera having the TTL type finder is free from the finder parallax because the photographing system and the observing system have a common optical axis. This constitutes a feature that, regardless of what values the object distance and the focal length take, exactly the same field of view as that seen in the finder can be photographed on the photosensitive surface (film surface).
Also, the photographing system forms a primary image whose frame is of almost the same size as that of the picture frame on the photosensitive surface, giving an additional feature that a finder image can be observed in a large frame.
In the case of employing the TTL type of optical finder, however, the particular requirement is to dispose the quick-return mirror or like mirror between the photographic lens and the focal plane to bend the optical path to the observing system. Therefore, this space cannot be occupied by the photographic lens. For example, the camera system using 35 mm film has to spare an axial length of usually 37-40 mm.
For this reason, the photographic lens must be designed always with the back focal distance assured to be more than a predetermined value. Hence, it has a tendency to increase the bulk and size of not only the photographic lens but also the camera as a whole.
The lens-shutter camera, on the other hand, has no requirement of providing a space for disposing a quick-return mirror. So, the back focal distance may be short at any rate provided the last lens surface does not come into contact with the photosensitive surface (focal plane). Hence, it has the advantage of achieving a minimization of the size of the lens itself and the whole camera.
Because the photographing system and the observing system have, however, different optical axes from each other, there exists a finder parallax.
Particularly when the focal length increases, the amount of parallax error compared to the film rapidly increases to an actually unacceptable level, and even more so when shortening of the object distance occurs simultaneously.
Meanwhile, in the latter classification, the camera which reproduces a record by using film, because the reproducibility of the image information is good owing to the film whose resolution is generally high, has a feature that it is well adapted to snap shots for recording.
However, the use of the film as the recording medium gives the reproducing method problems that the reproduction is limited to still pictures and that, because of the necessity of the developing process, it lacks instantaneity.
The electrical recording and reproducing method, on the other hand, obviates the necessity of carrying out the developing process. But, because the number of picture elements available in the photoelectric transducer means is relatively small, the quality of the reproduced image information is not always high enough, giving a problem that, for a given quality, the enlarging magnification to which, for example, a still picture is reproduced by expanding the image information for one field must be limited.
On account of such problems, for example, Japanese Laid-Open Patent Application No. Sho 63-156480 proposes a camera having a photographic lens for film photography and another photographic lens for video photography arranged independently of each other. This has a problem that the entirety of the apparatus has a large size, which would sacrifice the portability.
Particularly when a zoom lens is used as the photographic lens, as it implies that the two zoom lenses are positioned side by side, the problem of increasing the size of the whole camera not only becomes serious but also there arises an additional problem of increasing the complexity of the structure of the camera.
Also, Japanese Laid-Open Patent Application No. Sho 64-13532 proposes a device for selectively directing the image formed by one photographic lens to the film and an image pickup element by using a reflection mirror. But the use of the reflection mirror behind the photographic lens necessitates the creation of a long back focal distance in designing the photographic lens, as has been described before. Therefore, similar problems arise that the total length of the lens tends to get too long and that the camera itself is unavoidably of large size.